Influência da temperatura nos mecanismos de deformação em uma superliga Inconel 625 fabricada por fusão em leito de pó

Abstract

In the present work, the knowledge about mechanical deformation at room temperature (RT) and cryogenic temperature (CT) of an Inconel 625 superalloy processed via laser powder bed fusion (LPBF-LB/M) and subjected to heat treatments was deepened. The motivation for the study is based on the scarcity of data in the literature on the performance of this superalloy under cryogenic conditions, especially when produced by PBF-LB/M. The methodology was divided into four stages. Initially, the metal powder was characterized, and the analyses revealed typical aspects of its reuse. In the second stage, samples were manufactured with different process parameters, with a minority of them presenting lack of fusion porosity within the sample set. In the third stage, microstructural evaluation after heat treatments revealed that direct aging (E) from the as-manufactured condition (CF) maintained the columnar morphology with refined dendrites, promoting the precipitation of inter-dendritic carbides. Solubilization (S), in turn, was not effective in promoting complete recrystallization. However, the S+E sequence resulted in an equiaxial and homogeneous microstructure, evidencing the combined action of the two treatments in microstructural reconfiguration. In the tensile tests, it was observed that the CF and E conditions presented the highest values of yield strength (YS) and tensile strength (TS), with higher elongation for the CF condition. The S+E condition showed greater ductility in TC compared to E, attributed to greater plastic accommodation capacity. Under all conditions, the TC tests resulted in lower total elongation and quasi-brittle behavior, with fractures dominated by mode I crack propagation. The negative influence of lack of fusion porosity on crack nucleation was confirmed in the fracture surface analyses of the test specimens. In terms of deformation mechanisms, the formation of deformation twins was identified in grains oriented according to <112> in TA and <101> in TC, the latter associated with a higher Schmid factor. Analysis of the stress-strain curves revealed an increase in the strain hardening rate in TC for all conditions, with the highest strain hardening exponent observed for the S+E condition, while the E condition showed a higher initial strain hardening rate, associated with a higher density of discordances in the early stages of deformation.